The fabrication of field effect transistor semiconductor devices, such as metal-oxide-semiconductor field effect transistors (MOSFET), requires providing relatively uniform, defect-free silicon dioxide layers on the semiconductor substrate. In order to fabricate high-quality MOSFET devices, it has been necessary to employ a post-oxidation annealing process after growth of the silicon dioxide. Such post-oxidation annealing has generally been carried out in an "inert, oxygen-free" atmosphere such as in nitrogen or argon. These post-oxidation annealing processes are necessary in order to reduce the fixed charge of the formed silicon dioxide layer.
By way of example, annealing in nitrogen or argon at about 1 atmosphere pressure has commonly been carried out in a hot-wall annealing furnace at temperatures of about 900.degree. C. in order to reduce fixed charge densities to achieve proper MOSFET operation. However, these annealing procedures have tended to adversely affect the insulating or dielectric characteristics of the silicon dioxide and the reliability of the silicon dioxide layers over extended periods of time. For instance, post-oxidation annealing in nitrogen or argon atmospheres can result in an increase in breakdown and trapping problems of the silicon dioxide insulator. Such electrical degradation may be associated with the early stages of thermal decomposition of silicon dioxide on silicon at high temperatures. Along these lines, see Tromp, et al., Phys. Rev. Letters 55, 2332 (1985) ard M. Kobayashi, et al., Abstract No. 66 of the Electrochemical Society Spring Meeting, Toronto, 1985 (unpublished), page 94.
These results show that, under vacuum or argon annealing at high temperature, the chemical reaction of siliccn dioxide and silicon at high temperature causes oxide decomposition by the generation of a volatile product, silicon monoxide (SiO), leading eventually to the formation of voids completely through the oxide film and finally to complete removal of the oxide.
The consequences of the early stages of this reaction can be severe for the quality of thin insulators and associated devices, such as metal-semiconductor-oxide field effect transistors, because electrical defects will be produced well before the physical deterioration of the oxide (as voids). Two manifestations of electrical defects--low field breakdown and increased hole trapping--have been observed in systematic experimental studies of post-oxidation annealing under oxygen-deficient conditions; other types of electrical degradation may also take place.
Low field breakdown phenomena indicate an inability of the oxide to sustain the electric field which must be applied during device operation. When low field breakdown is a problem, the device will either not operate properly or will fail too soon in its planned lifetime.
When radiation is incident on SiO.sub.2, hole and electron pairs are generated in the SiO.sub.2. A very high fraction of the electrons leave the SiO.sub.2, whereas more holes are trapped at the Si--SiO.sub.2 interface. These trapped holes have a positive charge and change the device characteristics. A decrease in the hole trapping rate at the interface enables the device to withstand more radiation before the device characteristics change to an intolerable value.
It has been suggested to ion implant oxygen into silicon dioxide and then to subsequently anneal such in an attempt to reduce surface traps and increase mobility. Moreover, suggestions have been made to employ relatively large quantities of oxygen after post-oxidation annealing in order to increase the oxygen content of the silicon dioxide layer. Furthermore, Japanese Kokai No. 22862 suggests employing relatively high-pressure oxygen in order to provide higher density oxide layers.
Discussions of certain anneal treatments and the effect thereof can be found in Vormen, Appl. Phys. Letters 27, 152 (1975); Balk, et al., Solid State Electronics 27, p. 709 (1984); Montillo, et al., Journal Electrochemical Society, Vol. 118, p. 1463 (1971); and Ray, et al., Journal Electrochemical Society, Vol. 128, p. 2466 (1981).
The procedures suggested in the prior art employ high levels of oxygen and high pressures far above that required to minimize the deleterious effects of inert gas post-oxidation annealing, while in some cases (for example oxygen implantation) they degrade the insulator or substrate quality.